1. Field of the Invention
The present invention relates to a laser diode assembly and more particularly to a laser diode assembly which is capable of guiding a laser beam to a direction perpendicular to the surface of a mount unit of the assembly.
2. Description of the Related Art
An edge emitting laser diode is known as a kind of laser diode assembly that is used to guide a laser beam to a direction parallel to the surface of the assembly. In order to transmit the laser beam by employing other optical components, such as an optical fiber, to the edge emitting laser diode, it is necessary to arrange an optical coupling unit such as a lens or a waveguide, or the optical fiber directly. to a vicinity of an exit of the laser beam. This arrangement makes it impossible to secure enough room to dispose a drive circuit, a beam detecting element, a beam emitting element, or a wire onto the assembly. This limits the flexible of designing the assembly. In addition. it is also impossible to miniaturize the assembly. by integrating the elements and the wires onto the same assembly. This constraint of arrangement becomes remarkable when laser diodes are integrated in high density onto the assembly in array manner.
With a surface emitting laser diode, on the contrary, high flexibility in designing can be achieved on wiring and integration, because an optical path needs not employed on the assembly. This can be advantageous of miniaturization and cost-efficiency of the assembly.
In recent years, an optical transmission system has been widely developed in order to realize a optical-subscriber system in the telecommunication area. In the optical transmission system. if a plastic optical fiber having a larger diameter can be utilized, the laser diode and the plastic optical fiber can be coupled directly without employing lenses. Accordingly, the number of parts on the assembly can be reduced
To simulate a surface emitting laser diode, a mirror reflects a laser beam from an edge emitting laser diode to the perpendicular direction. A conventional (100) silicon substrate is usually employed as the mirror. However, a (111) surface, which corresponds to the mirror surface, is known to have 54.74 degree angle with respect to the (100) surface. This is described, for example, by Akio Yoshikawa. xe2x80x98Laser-Detector-Hologram Unit for Thin Optical Pick-up Head of a CD Playerxe2x80x99 IEEE Transactions on Components, Packaging, and Manufacturing Technology Part B, Vol. 18, No. 2, May 1995 pp245-249. In order to obtain the laser beam to the perpendicular direction, a mirror having 45 degrees with respect to the surface of the substrate is required. Thus. the (111) surface of the mirror is manufactured to be 9.74 degrees off the (100) surface.
However, when the 45-degree-mirror is manufactured by etching of the 9.74-degree-off-angled (100) silicon substrate, the other surface which is simultaneously produced by etching has a 9.74-degree-added angle surface. This means that a mirror having a 64.47 degree angle with respect to the surface of the substrate is produced. Such a mirror having a 64.47 degree angle cannot be used as the surface emitting laser diode. Therefore. the number of sub-mounts having a useable mirror from a silicon wafer is reduced. Moreover. because a detecting surface of a photo detector placed on the sub-mount and an edge surface of the optical fiber are disposed in parallel, a laser beam which does not enter the photo detector but is reflected by both an upper surface of the sub-mount and the edge surface of the optical fiber enters the laser diode. This destabilizes the output of the laser diode.
The above discussion is focused on only the case when the laser beam is guided to the perpendicular direction with respect to the surface of the substrate. However. it is also difficult to guide the laser beam to arbitrary direction other than the perpendicular direction, as long as using such conventional and inexpensive silicon wafer which has fixed off angle and surface orientation of crystal is used.
In the conventional laser diode assembly as stated above, the 9.74-degree-off-angled (100) silicon substrate is used to produce the 45-degree-mirror of the (111) surface. However, unnecessary 64.47-degree-surface is simultaneously produced, and this makes impossible to increase the number of the sub-mount to be manufactured from a silicon wafer and thereby involving cost-increasing.
The present invention has been made in view of the above-mentioned circumstances and is intended to solve the above-mentioned problems. In particular, one purpose of the present invention is to provide a laser diode assembly capable of guiding the laser beam to a predetermined direction by utilizing the mirror surface which has arbitrary angle with respect to the sub-mount.
Additional purposes and advantages of the invention will be apparent to persons skilled in this field from the following description, or may be learned by practice of the invention.
The present invention provides a laser diode assembly including: a first unit having a first surface and a mounting surface inclined to the first surface: a second unit made of a semiconductor substrate on the first unit, the second unit having a second surface and a reflecting surface that coincides with a (111) surface of the semiconductor substrate inclined to the second surface; and a laser diode on the second surface for irradiating a laser beam to the reflecting surface along a direction parallel to the second surface; wherein the second surface is parallel to the mounting surface and an angle between the reflecting surface and the first surface is substantially 45 degrees.
An inclined angle of the mounting surface with respect to the first surface may be 19.48 degrees. and an inclined angle of the reflected surface with respect to the second surface may be 54.74 degrees. Similarly, an inclined angle of the mounting surface with respect to the first surface may be 38.94 degrees, and an inclined angle of the reflected surface with respect to the second surface may be 64.47 degrees.
The reflecting surface may be formed by an etching process. The second unit may include silicon, and the second surface may be a (100) silicon surface. Gold may be evaporated on the reflecting surface.
A step may be formed by the first surface and the mounting surface, and the step may be used to adjust at least one portion of the second unit.
The laser diode may be integrally manufactured on the second unit. A photo detector for detecting an optical signal may be disposed on the second unit
An optical transceiver material may be disposed for guiding the laser beam to a predetermined position. The optical transceiver material may include an optical fiber. The laser diode may include a red semiconductor laser diode or a blue semiconductor laser diode.
The present invention also provides a mount unit including a first surface; and a mounting surface adjacent to the first surface, the angle between the first surface and the second surface being greater than 0 degree and less than 90 degrees, wherein a mounted unit on the mounting surface has a second surface parallel to the mounting surface and a reflecting surface adjacent to the second surface, the angle between the reflecting surface and the first surface being substantially 45 degrees.
The present invention further provides an optical head apparatus for recording/reproducing information onto/from an optical recording medium. including an optical head capable of moving relative to the optical recording medium, the optical head including a first unit having a first surface and a mounting surface inclined to the first surface; and a second unit comprising a semiconductor substrate on the first unit and having a second surface and a reflecting surface that coincides with a (111) surface of the semiconductor substrate inclined to the second surface; a laser diode on the second surface of the optical head for irradiating a laser beam to the reflecting surface along a direction parallel to the second surface; and a lens for condensing the laser beam onto the optical recording medium, wherein the second surface of the second unit is parallel to the mounting surface, and an angle between the reflecting surface and the first surface is substantially 45 degrees.
The present invention also provides a transceiver apparatus having at least a pair of terminals for transmitting/receiving optical information, the terminal includes: a first unit having a first surface and a mounting surface inclined to the first surface; a second unit made of a semiconductor substrate on the first unit, having a second surface and a reflecting surface that coincides with a (111) surface of the semiconductor substrate inclined to the second surface and a laser diode on the second surface for irradiating a laser beam to the reflecting surface along a direction parallel to the second surface: wherein the second surface is parallel to the mounting surface, and an angle between the reflecting surface and the first surface is substantially 45 degrees.
Further purposes, features and advantages of the invention will become apparent from the detailed description of preferred embodiments that allows, when considered together with the accompanying figures of drawings.